1. Field of the Invention
This invention relates to the registration of user identities in a communications system.
2. Description of the Related Art
FIG. 1 shows part of the architecture of the 3GPP system, including the IP Multimedia Subsystem (IMS) 1. The IMS includes a serving call session control function (S-CSCF) 2 which can communicate with a home subscriber server (HSS) 3 over a Cx-type interface. The system also includes one or more connection entities 4 such as packet switched domains or P-CSCFs by means of which the IMS 1 can communicate with user entities 5 such as mobile phones. The interface 6 between the S-CSCF 2 and the HSS 3 is a Cx-type interface, whose characteristics are tightly specified.
The general functionality of the units shown in FIG. 1 in a current 3G system is well-known. In particular, the S-CSCF provides services to the user entities and the HSS stores information on subscriptions which can be accessed by the S-CSCF and stored by it in a local database 7 for assisting the provision of services to users under that subscription.
The current specification for 3GPP Rel-6 TS 23.228 (version 6.7.0, chapter 4.3.3.4 FIG. 4.6) defines the IMS subscription, which may consist of multiple private user identities. The private user identities may be paired with dedicated or shared public user identities.
Currently the public user identity—private user identity pair is registered explicitly and it is assumed that the S-CSCF will find out about the pairing of a subscription's private user identities with the help of shared public user identity/identities when such are registered. In some situations this can work satisfactorily. However, the private user identities may have also dedicated public user identities, which may be registered independently of the shared public user identities. It has been identified that when this happens under the current design the S-CSCF has no means of finding out that parings of a registered public user identity with a private user identity belong to the same IMS subscription.
There is therefore a need for a means of enabling the S-CSCF to find out about such pairings.
WO 2004/000089 (US 2004/0196796) addresses problems associated with an HSS linking multiple user identities to the same subscriber. Such identities must be registered at the same S-CSCF and accordingly the HSS does not give server capabilities for the second and further registrations, but instead gives the name of the already used S-CSCF.